以下是在国外网站找到的相关技术资料，供你参考：
In the list of actions to be performed, some packages will be followed by one or
more characters enclosed in braces; for instance: “aptitude{u}”. These
characters provide extra information about the package’s state, and can include
any combination of the following:

‘a’: the package was automatically installed or removed.
‘b’: some of the package’s dependencies are violated by the proposed changes.
‘p’: the package will be purged in addition to being removed.
‘u’: the package is being removed because it is unused.